Energy- and electron-transfer systems in algal photosynthesis. I. Actions of two photochemical systems in oxidation-reduction reactions of cytochrome in Porphyra.

Abstract

Abstract 1. 1. The light-induced oxidation-reduction reactions of Porphyra-cytochrome-553 in the living thalli and isolated particles of three species of Porphyra ( P. yezoensis, P. tenera and P. suborbiculata ) were studied. 2. 2. The action spectrum of cytochrome oxidation had a maximum at 685–690 mμ. In the presence of background illumination of 680–700 mμ, photochemical reduction by a second light of wavelengths shorter than 650 mμ was observed. The maxima of the action spectrum for the reduction were located at 565 mμ and 615–620 mμ. This reduction of cytochrome by light absorbed by phycobilins was inhibited by 5-bromo-3-isopropyl-6-methyluracil 3(4′-chlorophenyl)-1,1-dimethylurea, 2-chloro-4,6-bis-(ethylamino)-1,3,5-triazine, 3,4-dichloropropionanilide and o -phenanthroline. These substances neither inhibited the light-induced oxidation of cytochrome, nor the dark reduction of cytochrome. In the presence of these substances, light-induced oxidation of cytochrome was observed on illumination of the light absorbed by phycobilins as well as by chlorophyll a . 3. 3. Effects of incident light intensity, dark period, inhibitors, gas phase, etc. on the rates and the steady-state change of the cytochrome reactions were investigated. 4. 4. Comparison of the observed amounts of cytochrome change and the amounts of cytochrome-553 extracted from the thalli indicated that the major portion of the cytochrome-553 present in the thalli changed its oxidation-reduction state on illumination. 5. 5. The quantum yield of cytochrome oxidation by light absorbed by chlorophyll a was about 0.14. In the presence of 5-bromo-3-isopropyl-6-methyluracil, quantum yields with light absorbed by chlorophyll a and with light absorbed by phycobilins were about 0.15 and 0.11, respectively.